Answer this question truthfully
### Question: What causes Amyotrophic lateral sclerosis?
### Response: In about 10% of cases, ALS is caused by a genetic defect. In the remaining cases, the cause is unknown.
In ALS, nerve cells (neurons) waste away or die, and can no longer send messages to muscles. This eventually leads to muscle weakening, twitching, and an inability to move the arms, legs, and body.
The condition slowly gets worse. When the muscles in the chest area stop working, it becomes hard or impossible to breathe on one's own.
ALS affects approximately 5 out of every 100,000 people worldwide.